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.\"     @(#)swapon.8	8.1 (Berkeley) 6/5/93
.\" $FreeBSD: src/sbin/swapon/swapon.8,v 1.15.2.2 2001/12/14 15:17:56 ru Exp $
.\"
.Dd September 7, 2010
.Dt SWAPON 8
.Os
.Sh NAME
.Nm swapon , swapoff , swapctl
.Nd "specify devices for paging and swapping"
.Sh SYNOPSIS
.Nm swapon Fl acEiq | Ar
.Nm swapoff Fl aq | Ar
.Nm swapctl
.Op Fl AeghklmsU
.Oo
.Fl a Ar
|
.Fl d Ar
.Oc
.Sh DESCRIPTION
The
.Nm swapon , swapoff
and
.Nm swapctl
utilities are used to control swap devices in the system.
At boot time all swap entries in
.Pa /etc/fstab
are added automatically when the system goes multi-user.
Swap devices use a fixed interleave; the maximum number of devices
is specified by the kernel configuration option
.Dv NSWAPDEV ,
which is typically set to 4.
There is no priority mechanism.
.Pp
The
.Nm swapon
utility adds the specified swap devices to the system.
If the
.Fl a
option is used, all swap devices in
.Pa /etc/fstab
will be added.
The following options are supported:
.Bl -tag -width indent
.It Dq noauto
The device is ignored and will not be added or removed with this option.
.It Dq crypt
Swap will be encrpted with a random key using a /dev/mapper name of
swap-<device> ,
for example 'swap-da0s1b'.
This will also load the dm_target_crypt module if necessary.
.It Dq trim
Swap will be TRIMed if the device supports it, otherwise this option
will be ignored.
.El
.Pp
If the
.Fl q
option is used informational messages will not be
written to standard output when a swap device is added.
If the
.Fl c
option is used, the device will be encrypted with a random
key.
If the
.Fl E
option is used, the device will be trimmed if
it supports trim and the trim_enabled sysctl is on.
The
.Fl i
option asks user confirmation before adding a swap device.
.Pp
The
.Nm swapoff
utility removes the specified swap devices from the system.
If the
.Fl a
option is used, all swap devices in
.Pa /etc/fstab
will be removed, unless their
.Dq noauto
option is also set.
If the
.Fl c
option is used the device is mapped to the appropriate crypto device
and the crypto device is removed as well.
If this option is specified in
.Nm swapon
then it should also be specified in
.Nm swapoff .
If the
.Fl q
option is used informational messages will not be
written to standard output when a swap device is removed.
Note that
.Nm swapoff
will fail and refuse to remove a swap device if there is insufficient
VM (memory + remaining swap devices) to run the system.
The
.Nm swapoff
utility
must move swapped pages out of the device being removed which could
lead to high system loads for a period of time, depending on how
much data has been swapped out to that device.
.Pp
The
.Nm swapctl
utility exists primarily for those familiar with other
.Bx Ns s
and may be
used to add, remove, or list swap devices.
Note that the
.Fl a
option is used differently in
.Nm swapctl
and indicates that a specific list of devices should be added.
The
.Fl d
option indicates that a specific list should be removed.
The
.Fl A
and
.Fl U
options to
.Nm swapctl
operate on all swap entries in
.Pa /etc/fstab
which do not have their
.Dq noauto
option set.
.Pp
Swap information can be generated using the
.Xr swapinfo 8
utility,
.Nm pstat
.Fl s ,
or
.Nm swapctl
.Fl l .
The
.Nm swapctl
utility has the following options for listing swap:
.Bl -tag -width indent
.It Fl h
Output values in human-readable form.
.It Fl g
Output values in gigabytes.
.It Fl k
Output values in kilobytes.
.It Fl m
Output values in megabytes.
.It Fl l
List the devices making up system swap.
.It Fl s
Print a summary line for system swap.
.It Fl c
The swap is or should be crypted.
.It Fl e , Fl E
Attempts to Trim the device if -[Aa] is used.  The lower-case version
of this option is deprecated.
.It Fl i
Asks user confirmation when -a is used.
.It Fl q
Less noisy output.
.Pp
The
.Ev BLOCKSIZE
environment variable is used if not specifically
overridden.
1K blocks are used by default.
.El
.Sh FILES
.Bl -tag -width ".Pa /dev/{ad,da}?s?b" -compact
.It Pa /dev/{ad,da}?s?b
standard paging devices
.It Pa /dev/vn?s?b
vnode disk paging device
.It Pa /etc/fstab
ASCII filesystem description table
.It Pa /etc/vntab
ASCII vnode file table
.El
.Sh DIAGNOSTICS
These utilities may fail for the reasons described in
.Xr swapon 2 .
.Sh SEE ALSO
.Xr swapon 2 ,
.Xr fstab 5 ,
.Xr init 8 ,
.Xr pstat 8 ,
.Xr rc 8 ,
.Xr vnconfig 8
.Sh HISTORY
The
.Nm swapon
utility appeared in
.Bx 4.0 .
The
.Nm swapoff
and
.Nm swapctl
utilities appeared in
.Fx 5.1
and were later ported to
.Dx 2.7 .